import cv2 as cv
import numpy as np

img = cv.imread('../resources/miku.jpg')
# bgr -> rgb
dst = np.zeros_like(img)
cv.mixChannels([img], [dst], fromTo=[2, 0, 1, 1, 0, 2])
cv.imshow('dst', dst)

cv.waitKey(0)
cv.destroyAllWindows()